HR: 0800h
AN: V11D-0809    [Abstracts]
TI: Investigations of CO2 Emissions From Holocene Volcanic Features of Mono Lake and the Mono Craters Volcanic Chain in Eastern California
AU: * Bergfeld, D
EM: dbergfel@usgs.gov
AF: U.S. Geological Survey, MS 910 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Howle, J F
EM: jfhowle@usgs.gov
AF: U.S. Geological Survey, PO Box 1360, Carnelian Bay, CA 96140, United States
AU: Evans, W C
EM: wcevans@usgs.gov
AF: U.S. Geological Survey, MS 910 345 Middlefield Road, Menlo Park, CA 94025, United States
AB: Magmatic CO₂ emissions have been well studied at the Long Valley caldera in eastern California, but not along the much younger and voluminous Mono Craters volcanic chain 10 to 20 km to the north. A June 2007 field investigation to identify and quantify emissions of magmatic CO₂ focused on some of the youngest eruptive features in the chain and on Paoha Island in Mono Lake. North Coulee (NC) is one of the larger late-Holocene volcanic features in the Mono Craters chain and is composed primarily of a glassy rhyolite flow that is partially blanketed on the west by tephra deposits. There is no soil development at NC, and vegetation is generally limited to a few scattered pine trees. Portions of NC contain discrete zones of discolored altered rock that provide evidence of former fumarolic activity; however in this study, only one small area displayed temperatures greater than 40° C. CO₂ flux was measured at 224 sites over a ~ 244, 000 m² area that included many of the alteration zones. The CO₂ flux at most sites was anomalously high, with an average flux over the entire study area of 109 gm^-2d^-1. The estimated discharge of CO₂ is around 27 t d^-1. Biogenic CO₂ emissions at NC should be essentially zero because of the scarcity of soil and vegetation. Given that 63 sites had fluxes below detection limits this supposition is well supported. Additional gas chemistry and isotope work will help determine if all the CO₂ is derived from magma. If so, then the magmatic CO₂ output from NC is comparable to the CO₂ output from the Long Valley hydrothermal system. Diffuse CO₂ emissions were also measured at two locations on Paoha Island: around the young cinder cone on the north end of the island, and over dacite flows adjacent to Hot Springs Cove (HSC) on the east. The survey revealed no detectable flux of CO₂ around the cinder cone. At HSC, CO₂ emissions were localized around steam vents and were generally low. The average flux from 25 sites was less than 8 gm^{- 2}d^-1 with only 4 sites displaying an anomalous flux greater than 15 gm^-2d^-1. These data are in agreement with results from gas samples collected from bubbling springs along the shore of HSC, which contain predominantly C₁ through C₆ hydrocarbons and N₂ with less than 4% CO₂.
DE: 8419 Volcano monitoring (7280)
DE: 8430 Volcanic gases
DE: 8486 Field relationships (1090, 3690)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting